contact lens case reports

Elevating Our Knowledge
Of the Corneal Surface

Elevation maps describe the height (elevation) of the cornea in microns from a reference surface commonly called the "reference sphere" (Figure 1). It's similar to viewing the fluorescein pattern
of a spherical rigid gas permeable lens in that areas of the cornea that fall below the best fit sphere (fluorescein pooling) are noted in negative microns and correspond to the blue or cooler colors of the map. Areas of the cornea higher than the reference sphere (corneal thinning) are noted in positive microns and correspond to the red or hotter colors of the map.

Figure 1. The reference sphere superimposed through the cornea.

This can create some confusion in that practitioners are used to axial maps in which the hotter colors are steeper and the cooler colors are flatter. Elevation maps measure the difference between the modal (reference sphere) and the actual corneal surface in microns of height, not diopters of curvature.